SIST EN 61000-4-7:2003
(Main)Electromagnetic compatibility (EMC) -- Part 4-7: Testing and measurement techniques - General guide on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected thereto
Electromagnetic compatibility (EMC) -- Part 4-7: Testing and measurement techniques - General guide on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected thereto
Applies to instrumentation intended for measuring spectral components in the frequency range up to 9 kHz which are superimposed on the fundamental of the power supply systems at 50 Hz and 60 Hz. For practical considerations, this standard distinguishes between harmonics, interharmonics and other components above the harmonic frequency range, up to 9 kHz. Defines the measurement instrumentation intended for testing individual items of equipment in accordance with emission limits given in certain standards (for example, harmonic current limits as given in EN 61000-3-2) as well as for the measurement of harmonic currents and voltages in actual supply systems.
Elektromagnetische Verträglichkeit (EMV) -- Teil 4-7: Prüf- und Messverfahren - Allgemeiner Leitfaden für Verfahren und Geräte zur Messung von Oberschwingungen und Zwischenharmonischen in Stromversorgungsnetzen und angeschlossenen Geräten
Compatibilité électromagnétique (CEM) -- Partie 4-7: Techniques d'essai et de mesure - Guide général relatif aux mesures d'harmoniques et d'interharmoniques, ainsi qu'à l'appareillage de mesure, applicable aux réseaux d'alimentation et aux appareils qui y sont raccordés
S'applique à l'instrumentation destinée à mesurer les composantes spectrales dans la gamme de fréquence allant jusqu'à 9 kHz, qui se superposent au fondamental des réseaux d'alimentation à 50 Hz et 60 Hz. Pour des raisons pratiques, la présente norme établit une distinction entre les harmoniques, les interharmoniques et les composantes au-delà de la plage de fréquence harmonique, jusqu'à 9 kHz. Définit l'instrumentation de mesure destinée aux essais d'appareils individuels conformément aux limites d'émission données dans certaines normes (par exemple, les limites de courant harmonique données dans la EN 61000-3-2) ainsi qu'à la mesure des courants et tensions harmoniques sur les réseaux d'alimentation eux-mêmes.
Electromagnetic compatibility (EMC) - Part 4-7: Testing and measurement techniques - General guide on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected thereto (IEC 61000-4-7:2002)
General Information
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Standards Content (Sample)
SLOVENSKI SIST EN 61000-4-7:2003
STANDARD
december 2003
Electromagnetic compatibility (EMC) - Part 4-7: Testing and measurement
techniques - General guide on harmonics and interharmonics measurements and
instrumentation, for power supply systems and equipment connected thereto (IEC
61000-4-7:2002)
ICS 33.100.20 Referenčna številka
SIST EN 61000-4-7:2003(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
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EUROPEAN STANDARD EN 61000-4-7
NORME EUROPÉENNE
EUROPÄISCHE NORM October 2002
ICS 33.100.10; 33.100.20 Supersedes EN 61000-4-7:1993
English version
Electromagnetic compatibility (EMC)
Part 4-7: Testing and measurement techniques -
General guide on harmonics and interharmonics
measurements and instrumentation,
for power supply systems and equipment connected thereto
(IEC 61000-4-7:2002)
Compatibilité électromagnétique (CEM) Elektromagnetische Verträglichkeit (EMV)
Partie 4-7: Techniques d'essai Teil 4-7: Prüf- und Messverfahren -
et de mesure - Allgemeiner Leitfaden für Verfahren
Guide général relatif aux mesures und Geräte zur Messung
d'harmoniques et d'interharmoniques, von Oberschwingungen und
ainsi qu'à l'appareillage de mesure, Zwischenharmonischen in
applicable aux réseaux d'alimentation Stromversorgungsnetzen und
et aux appareils qui y sont raccordés angeschlossenen Geräten
(CEI 61000-4-7:2002) (IEC 61000-4-7:2002)
This European Standard was approved by CENELEC on 2002-10-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2002 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61000-4-7:2002 E
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EN 61000-4-7:2002 - 2 -
Foreword
The text of document 77A/382/FDIS, future edition 2 of IEC 61000-4-7, prepared by SC 77A, Low
frequency phenomena, of IEC TC 77, Electromagnetic compatibility, was submitted to the
IEC-CENELEC parallel vote and was approved by CENELEC as EN 61000-4-7 on 2002-10-01.
This European Standard supersedes EN 61000-4-7:1993.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2003-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-10-01
Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annex ZA is normative and annexes A, B and C are informative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61000-4-7:2002 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 61000-3 (Series) NOTE Partly harmonized in EN 61000-3 series (not modified).
IEC 61010-1 NOTE Harmonized as EN 61010-1:2001 (not modified).
__________
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- 3 - EN 61000-4-7:2002
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
1)
IEC 60050-161 - International Electrotechnical - -
Vocabulary (IEV)
Chapter 161: Electromagnetic
compatibility
1) 2)
IEC 61000-3-2 - Electromagnetic compatibility (EMC) EN 61000-3-2 2000
Part 3-2: Limits - Limits for harmonic
current emissions (equipment input
current up to and including 16 A per
phase)
1) 2)
IEC 61967-1 - Integrated circuits - Measurement of EN 61967-1 2002
electromagnetic emissions, 150 kHz to
1 GHz
Part 1: General conditions and
definitions
1)
Undated reference.
2)
Valid edition at date of issue.
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INTERNATIONAL IEC
STANDARD 61000-4-7
Second edition
2002-08
BASIC EMC PUBLICATION
Electromagnetic compatibility (EMC) –
Part 4-7:
Testing and measurement techniques –
General guide on harmonics and interharmonics
measurements and instrumentation, for power
supply systems and equipment connected thereto
” IEC 2002 Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical,
including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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For price, see current catalogue
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61000-4-7 © IEC:2002 – 3 –
CONTENTS
FOREWORD . 7
INTRODUCTION .11
1 Scope .13
2 Normative references.13
3 Definitions, symbols and indices .15
3.1 Definitions related to frequency analysis.15
3.2 Definitions related to harmonics.17
3.3 Definitions related to distortion factors.19
3.4 Definitions related to interharmonics.21
3.5 Notations .23
3.5.1 Symbols and abbreviations .23
3.5.2 Indices.25
4 General concepts and common requirements for all types of instrumentation.25
4.1 Characteristics of the signal to be measured .25
4.2 Accuracy classes of instrumentation .25
4.3 Types of measurement .25
4.4 General structure of the instrument.27
4.4.1 Main instrument .27
4.4.2 Post-processing parts .29
5 Harmonic measurements .31
5.1 Current input circuit .31
5.2 Voltage input circuit .31
5.3 Accuracy requirements .33
5.4 Measurement set-up for emission assessment.35
5.5 Assessment of harmonic emissions .37
5.5.1 Grouping and smoothing .39
5.5.2 Compliance with emission limits.41
5.6 Assessment of voltage harmonic subgroups .41
6 Other analysis principles.41
7 Transitional period .43
8 General .43
Annex A (informative) Measurement of interharmonics.45
Annex B (informative) Measurements above the harmonic frequency range up to 9 kHz.49
Annex C (informative) Technical considerations for grouping method .53
Bibliography.71
Figure 1 – General structure of the measuring instrument .29
Figure 2 – Measurement set-up for single-phase emission measurement .35
Figure 3 – Measurement set-up for three-phase emission measurements.35
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61000-4-7 © IEC:2002 – 5 –
Figure 4 – Illustration of harmonic and interharmonic groups (shown here for a 50 Hz
supply) .39
-1
Figure 5 – Realisation of a digital low-pass filter: z designates a time window delay,
α and β are the filter coefficients (see table 2 for values) .39
Figure 6 – Illustration of a harmonic subgroup and an interharmonic centred subgroup
(of a 50 Hz supply).41
Figure B.1 – Illustration of frequency bands for measurement, in the range 2 kHz to
9 kHz .51
Figure C.1 – Large 5th harmonic current fluctuation .59
Figure C.2 – Large 5th harmonic voltage fluctuation.59
Figure C.3 – Fluctuating 3rd harmonic current of a micro-wave appliance .61
Figure C.4 – Communication signal of 178 Hz together with 3rd and 5th harmonics .63
Figure C.5 – Interharmonic at 287 Hz, 5th and 6th harmonic .63
Figure C.6 – Modulated 5th harmonic and interharmonic at 287 Hz .67
Figure C.7 – Component vectors at frequencies of 245 Hz and 255Hz.69
Table 1 – Accuracy requirements for current, voltage and power measurements .33
Table 2 – Smoothing filter coefficients according to the window width .43
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61000-4-7 © IEC:2002 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROMAGNETIC COMPATIBILITY (EMC) –
Part 4-7: Testing and measurement techniques –
General guide on harmonics and interharmonics measurements and
instrumentation, for power supply systems and
equipment connected thereto
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international co-operation on all questions concerning standardization in the electrical and electronic
fields. To this end and in addition to other activities, the IEC publishes International Standards. Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt
with may participate in this preparatory work. International, governmental and non-governmental
organizations liaising with the IEC also participate in this preparation. The IEC collaborates closely with the
International Organization for Standardization (ISO) in accordance with conditions determined by agreement
between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has
representation from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the
form of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the
subject of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61000-4-7 has been prepared by subcommittee 77A: Low
frequency phenomena, of IEC technical committee 77: Electromagnetic compatibility.
This standard forms part 4-7 of IEC 61000. It has the status of a basic EMC publication in
accordance with IEC Guide 107.
This second edition cancels and replaces the first edition published in 1991, and constitutes a
technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
77A/382/FDIS 77A/387/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.
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61000-4-7 ” IEC:2002 – 9 –
Annexes A, B and C are for information only.
The committee has decided that the contents of this publication will remain unchanged until
2005. At this date, the publication will be
x reconfirmed;
x withdrawn;
x replaced by a revised edition, or
x amended.
The contents of the corrigendum of July 2004 have been included in this copy.
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61000-4-7 © IEC:2002 – 11 –
INTRODUCTION
IEC 61000 is published in separate parts, according to the following structure:
Part 1: General
General considerations (introduction, fundamental principles)
Definitions, terminology
Part 2: Environment
Description of the environment
Classification of the environment
Compatibility levels
Part 3: Limits
Emission limits
Immunity limits (in so far as they do not fall under the responsibility of the product
committees)
Part 4: Testing and measurement techniques
Measurement techniques
Testing techniques
Part 5: Installation and mitigation guidelines
Installation guidelines
Mitigation methods and devices
Part 6: Generic standards
Part 9: Miscellaneous
Each part is further subdivided into several parts, published either as International Standards
or as technical specifications or technical reports, some of which have already been published
as sections. Other will be published with the part number followed by a dash and a second
number identifying the subdivision (example: 61000-6-1).
These publications will be published in chronological order and numbered accordingly.
This part is an International Standard for the measurement of harmonic currents and voltages
in power supply systems and harmonic currents emitted by equipment. It also specifies the
performance of a standard measuring instrument.
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61000-4-7 © IEC:2002 – 13 –
ELECTROMAGNETIC COMPATIBILITY (EMC) –
Part 4-7: Testing and measurement techniques –
General guide on harmonics and interharmonics measurements and
instrumentation, for power supply systems and
equipment connected thereto
1 Scope
This part of IEC 61000 is applicable to instrumentation intended for measuring spectral
components in the frequency range up to 9 kHz which are superimposed on the fundamental
of the power supply systems at 50 Hz and 60 Hz. For practical considerations, this standard
distinguishes between harmonics, interharmonics and other components above the harmonic
frequency range, up to 9 kHz.
This standard defines the measurement instrumentation intended for testing individual items
of equipment in accordance with emission limits given in certain standards (for example,
harmonic current limits as given in IEC 61000-3-2) as well as for the measurement of
harmonic currents and voltages in actual supply systems. Instrumentation for measurements
above the harmonic frequency range, up to 9 kHz is tentatively defined (see Annex B).
NOTE 1 This document deals in detail with instruments based on the discrete Fourier transform.
NOTE 2 The description of the functions and structure of the measuring instruments in this standard is very
explicit and meant to be taken literally. This is due to the necessity of having reference instruments with
reproducible results irrespective of the characteristics of the input signals.
NOTE 3 The instrument is defined to accommodate measurements of harmonics up to the 50th order.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-161, International Electrotechnical Vocabulary – Chapter 161: Electromagnetic
compatibility
IEC 61000-3-2, Electromagnetic compatibility (EMC) – Part 3-2: Limits – Limits for harmonic
current emissions (equipment input current ≤16 A per phase)
IEC 61967-1, Integrated circuits – Measurement of electromagnetic emissions, 150 kHz to
1
1 GHz – Part 1: Measurement conditions and definitions
___________
1
To be published
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61000-4-7 ” IEC:2002 – 15 –
3 Definitions, symbols and indices
For the purposes of this part of IEC 61000, the definitions given in IEC 60050-161 (IEV) and
the following, apply.
3.1 Definitions related to frequency analysis
Notations: The following notations are used in the present guide for the Fourier series
development because it is easier to measure phase angles by observations of the zero
crossings:
f
m
§·
ft() c c sin ZMt (1)
01¦mm
¨¸
N
©¹
m 1
22
cb ja ab
mm m m m
°
c
°
m
C
m
°
2
°
°
with: (2)
§·
® a
m
M tarctan if b 0
¨¸
mm
°
b
©¹m
°
°
§·
a
m
°MS arctan if b 0
mm¨¸
b
°
©¹m
¯
T
w
2 m
§ ·
°
b f (t)u sin¨ Z t¸ dt
m 1
³
° T N
© ¹
w
0
°
T
°
w
° 2 § m ·
and: a f (t)ucos Z t dt (3)
¨ ¸
®
m 1
³
T N
© ¹
w
°
0
°
T
w
°
1
c f (t) dt
°
0
³
T
°
w
0
¯
where
Z is the angular frequency of the fundamental (Z = 2Sf );
1 1 1
T is the width (or duration) of the time window (T = NT ; T = 1/f ); the time window is
w w 1 1 1
that time span of a time function over which the Fourier transform is performed;
m
c is the amplitude of the component with frequency f f ;
m 1
m
N
N is the number of fundamental periods within the window width;
c is the d.c. component;
0
m is the ordinal number (order of the spectral line) related to the frequency basis
(f= 1/Tw).
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61000-4-7 © IEC:2002 – 17 –
NOTE 1 Strictly speaking these definitions apply to steady-state signals only.
The Fourier series is actually in most cases performed digitally, i.e. as a discrete Fourier transform (DFT).
The analogue signal f(t) to be analysed is sampled, A/D-converted and stored. Each group of M samples forms a
time window on which DFT is performed. According to the principles of Fourier series expansion, the window width
T determines the frequency resolution f = 1/T (i.e. the frequency separation of the spectral lines) for the
w w w
analysis and thus the frequency basis for the result of the transform. Therefore, the window width T must be an
w
integer multiple N of the fundamental period T of the system voltage: T = N × T . The sampling rate is in this case
1 w 1
f = M/(NT ) (where M = number of samples within T ).
s 1 w
Before DFT-processing, the samples in the time window T are often weighted by multiplying them with a special
w
symmetrical function "windowing function"). However, for periodic signals and synchronous sampling, it is
preferable to use a rectangular weighting window which multiplies each sample by unity.
The DFT-processor yields the orthogonal Fourier-coefficients a and b of the corresponding harmonic frequencies
m m
i
f = m/T , m= 0, 1, 2.2 -1. However, only m values up to half of the maximum value are useful, the other half just
m w
duplicates them.
When there is sufficient synchronisation, the harmonic order n related to the fundamental frequency f is given by
1
n = m/N (N = number of periods in T .).
w
NOTE 2 The fast Fourier transform (FFT) is a special algorithm allowing short computation times. It requires that
i
the number of samples M be an integer power of 2, M = 2 , with i ≥ 10 for example.
3.2 Definitions related to harmonics
3.2.1
harmonic frequency
f
n
frequency which is an integer multiple of the power supply (fundamental) frequency
(f = n × f )
n 1
3.2.2
harmonic order
n
(integer) ratio of a harmonic frequency to the power-supply frequency. In connection with the
analysis using DFT and synchronisation between f and f (sampling rate), the harmonic order
1 s
n is given by n = k/N (k = number of the Fourier component, N = number of periods T in T )
1 w
3.2.3
r.m.s. value of a harmonic component
G
n
r.m.s. value of one of the components having a harmonic frequency in the analysis of a non-
sinusoidal waveform
For brevity, such a component may be referred to simply as a 'harmonic'
NOTE 1 The harmonic component G is identical with the spectral component C with k = N × n; (G = C ). It is
n k n Nn
replaced, as required, by the symbol I for currents or by the symbol U for voltages.
n n
NOTE 2 The symbol C represents the r.m.s. value of the spectral component C for m = k in equation 2.
k m
NOTE 3 For the purposes of this standard, the time window has a width of N = 10 (50 Hz systems) or N = 12
(60 Hz systems) fundamental periods, i.e. approximately 200 ms (see 4.4.1). This yields G = C (50 Hz systems)
n 10n
and G = C (60 Hz systems).
12
n n
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61000-4-7 © IEC:2002 – 19 –
3.2.4
r.m.s. value of a harmonic group
G
g,n
square root of the sum of the squares of the r.m.s. value of a harmonic and the spectral
components adjacent to it within the time window, thus summing the energy contents of the
neighbouring lines with that of the harmonic proper. See also equation 8 and figure 4. The
harmonic order is given by the harmonic considered
3.2.5
r.m.s. value of a harmonic subgroup
G
sg,n
square root of the sum of the squares of the r.m.s. value of a harmonic and the two spectral
components immediately adjacent to it. For the purpose of including the effect of voltage
fluctuation during voltage surveys, a subgroup of output components of the DFT is obtained
by summing the energy contents of the frequency components directly adjacent to a harmonic
with that of the harmonic proper. (See also equation 9 and figure 6.) The harmonic order is
given by the harmonic considered
3.3 Definitions related to distortion factors
3.3.1
total harmonic distortion
THD
THD (symb.)
ratio of the r.m.s. value of the sum of all the harmonic components (G ) up to a specified
n
order (H) to the r.m.s. value of the fundamental component (G ):
1
2
H
§·G
n
THD = (4)
¦¨¸
G
n=2
©¹1
NOTE 1 The symbol G represents the r.m.s. value of the harmonic component (see 3.2.3). It is replaced, as required, by
the symbol I for currents or by the symbol U for voltages.
NOTE 2 The value of H is defined in each standard concerned with limits (IEC 61000-3 series).
3.3.2
group total harmonic distortion
THD
THDG (symb.)
ratio of the r.m.s. value of the harmonic groups (g) to the r.m.s. value of the group associated
with the fundamental:
2
H
§·G
gn
THDG = (5)
¨¸
¦
¨¸
G
n=2
g1
©¹
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61000-4-7 © IEC:2002 – 21 –
3.3.3
subgroup total harmonic distortion
THDS
THDS (symb.)
ratio of the r.m.s. value of the harmonic subgroups (sg) to the r.m.s. value of the subgroup
associated with the fundamental:
2
H
§·
G
sgn
THDS = (6)
¨¸
¦
¨¸
G
n=2 sg1
©¹
3.3.4
partial weighted harmonic distortion
PWHD
PWHD (symb.)
ratio of the r.m.s. value, weighted with the harmonic order n, of a selected group of higher
order harmonics (from the order H to H to the r.m.s. value of the fundamental:
min max
2
H
max
§·G
n
PWHD = n (7)
¦ ¨¸
G
nH=
©¹1
min
NOTE 1 The concept of partial weighted harmonic distortion is introduced to allow for the possibility of specifying
a single limit for the aggregation of higher order harmonic components.The partial weighted group harmonic
distortion can be evaluated by replacing the quantity G by the quantity G . The partial weighted subgroup
n g,n
harmonic distortion can be evaluated by replacing the quantity G by the quantity G .
n sg,n
NOTE 2 The values of H and H are defined in each standard concerned with limits (IEC 61000-3-series).
min max
NOTE 3 PWHD is defined in this standard because it is used in IEC 61000-3-4 and in IEC 61000-3-2 Ed. 2 with
amendment 1.
3.4 Definitions related to interharmonics
3.4.1
r.m.s. value of an interharmonic component
r.m.s. value of a spectral component of an electrical signal with a frequency between two
consecutive harmonic frequencies (see figure 4)
NOTE 1 The frequency of the interharmonic component is given by the frequency of the spectral line. This
frequency is not an integer multiple of the fundamental frequency.
NOTE 2 The frequency interval between two consecutive spectral lines is the inverse of the width of the time
window, approximately 5 Hz for the purposes of this standard.
NOTE 3 For the purposes of this standard, the interharmonic component is assumed to be the spectral
component C for k ≠ n × N.
k
3.4.2
r.m.s. value of an interharmonic group
C
ig,n
r.m.s. value of all interharmonic components in the interval between two consecutive
harmonic frequencies (see figure 4)
NOTE For the purposes of this standard, the r.m.s. value of the interharmonic group between the harmonic orders
n and n + 1 is designated as 'C '; for example, the group between n = 5 and n = 6 is designated as C .
ig,n ig,5
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61000-4-7 © IEC:2002 – 23 –
3.4.3
r.m.s. value of an interharmonic centred subgroup
C
isg,n
r.m.s. value of all interharmonic components in the interval between two consecutive
harmonic frequencies, excluding frequency components directly adjacent to the harmonic
frequencies (see figure 6)
NOTE For the purposes of this standard, the r.m.s. value of the centred subgroup between the harmonic orders n
and n + 1 is designated as 'C '; for example, the centred subgroup between n = 5 and n = 6 is designated as
isg,n
C .
isg,5
3.4.4
interharmonic group frequency
f
ig,n
mean of the two harmonic frequencies between which the group is situated
...
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